To assess the prevalence of gallstone disease and the behavior of gallbladder (GB) volume in childhood and adolescence, an ultrasonographic survey was carried out on 1570 subjects (age range 6-19 yr). Entered in the study were 750 males and 752 females (attendance rate, 95.7%). Gallstones were detected in two females aged 13 and 18 yr, respectively. None of the subjects in the study population had undergone cholecystectomy. The overall prevalence of gallstone disease was equal to 0.13% (0.27% in the female sex). A positive family history for biliary calculous disease was present in one of the two lithiasic girls. A progressive increase of GB volume with age was observed in both sexes, and figures were greater in males, than in age-matched females. A positive and statistically significant relationship was found between GB volume and body mass index (BMI) in both sexes. Obesity was recognized in 188 males (25.3%) and 167 females (25.0%). Obese subjects exhibited larger GB volumes than the nonobese age- and sex-matched controls. The study supports the view of a very low prevalence of gallstone disease in people younger than 20. It also provides information on GB size in relation to age, sex, and BMI.